Leather

ABSTRACT

An improved iron tanned leather is produced by the use of a novel acidic aqueous solution containing ferric iron and citric acid as essential ingredients. Optionally, glycerine may be added. This solution is used substantially according to known tanning procedures. The novel leather obtained is characterized by a pleasing light-fast, tan color, a shrink temperature which compares favorably with that required of the more expensive chrome tanning and stability of aging. On ashing at 1,000*C. in air the leather leaves an 8 to 17 percent by weight residue which is at least 90 percent ferric oxide.

United States Patent 11 1 Conklin 1 LEATHER [76] Inventor: Alfred R.Conklin, Rt. 4,

Harr odsburg, K y 403 [22] Filed: Aug. 13, 1971 21 Appl.No.: 171,752

OTHER PUBLICATIONS Chambard et al., I 3ulletin de lAssocia ti onFrancaise des Chimistes desIndiistiEBiiCuir, i6 Annee, No. 2-3, Feb-Mar.1954. Dawson; W. O. Journal of American Leather Chemists Assocn., July1952, pages 457, 458, 468.

11 3,837,797 14 1 Sept. 24, 1974 Kanagy et al., Journal of the Societyof Leather Trades Chemists, May 1944, page 121.

Chemical Abstracts, 1954, I3249d.

Primary ExaminerLeon D. Rosdol Assistant Examiner-H. Wolman Attorney,Agent, or FirmFrank W. Lane 57 ABSTRACT An improved iron tanned leatheris produced by the use of a novel acidic aqueous solution containingferric iron and citric acid as essential ingredients. Optionally,glycerine may be added. This solution is used substantially according toknown tanning procedures. The novel leather obtained is characterized bya pleasing light-fast, tan color, a shrink temperature which comparesfavorably with that required of the more expensive chrome tanning andstability of aging. On ashing at 1,000C. in air the leather leaves an 8to 17 percent by weight residue which is at least 90 percent ferricoxide.

6 Claims, N0 Drawings SUMMARY tric acid combination as well as the addedimprovement obtained by the use of glycerine. Tests under columns A, Band G illustrate the invention. In these columns in Table l the volumesof the solutions used along The Solutions 5 with the weights of reagentsused are listed. The con- The solutions of this invention to be used fortanning Centrations of the reagents are calculated from these containwater, ferric iron supplied in the form of ferric values. The procedureinvolved placing fifteen grams of chloride, and citric acid as theprimary essential ingrebate a d pickled Sheepskin in each of Seven 400ml. clients. The amount of ferric chloride is in the range of beakersand covering each with one of the solutions as from 30 to 70 grams perliter of the solution and the citlisted in the table. The skin wasstirred in the solution ric acid ranges from to grams per liter.Preferred and allowed to stand over night at room temperature. rangesare respectively from to 55 grams per liter Sodium carbonate solutionwas then added slowly to and 15 to 25 grams per liter. Glycerine up t 30grams each until the pH was raised to about 4.5 and remained per litermay be added to obtain additional improve- *a t s al r 0 m t sh s aremoved, ment. These various solutions are quite acid. The ex- 15 Washedby hand and squeezed dry, treated with glycercess acid may be partiallyneutralized to a pH under 2 inc and then with mineral oil and tacked toa drying with the usual alkaline agents prior to impregnating the Aftery g Samples A, B and G were found P skin to be tanned. Thispre-neutralization is not essenable, and Of a medium tan 001013 Shrinktests were ri l b t it i f d made and the results shown in the table.Sample A was 20 kept 2 years and re-examined. It appeared generally theTANNING PROCESS same with respect to color, feel, and pliability, andhad Tanning is accomplished by immersing the skin in the the same shrinktemperature. Sample showed no evichosen solution at a temperature notover 100F. long dance fbeiI 1g tanned f p G "l to Show enough toimpregnate. Th ki i prepared f hi that the preliminary partialneutrallzauon of the solustep the usual methods Following impregnationthe 25 U011 18 not necessary for the SUCCESS Of the process.

TABLE I A B C D E F G Total Volume, ml. 240 200 150 140 240 240 190 gms.FeCl l0 l0 l0 0 l0 l0 10 Cone. gm/l 41.6 50.0 56.7 0 41.6 41.6 52.6Citric acid, girls. 5 5 0 5 0 0 5 Cone. gm/l 20.8 25.0 0 35.7 0 0 26.3Glycerine, gms. 4 0 0 4 4 4 4 Cone. gm/l 16.7 0 0 28.5 l6.7 16.7 21.0Tartaric acid, gms. 0 0 0 0 5 0 0 Cone. gm/l 20.8

Oxalic acid, gms. 0 0 0 0 0 0 Cone. gm/l 20.8 Na Co gms. 5 5 5 5 5 0Cone. gm/l 20.8 25.0 33.3 35.7 20.8 20.8

pH of solu. 0.4 ash in leather 13.7 Shrink Temperature 212 200 170 170170 200 solution in contact with the skin is neu trali zed witli soEXAMPLE II dlum carbonate to a pH 1n the 3 to 6 range. The result- Thisexample shows the effect of using a by product mg leather washed andfimshed by known ferric chloride obtained from the chlorination ifilmenmeans' tie for the purpose of manufacturing titanium tetra- THELEATHER chloride. Two tanning solutions were made up identically exceptthat one solution contained laboratory The leather bl by the above P F hh grade ferric chloride and the other the by-product. The usual goodqual1t1es of tanned leather. It is unlque in composition of the Solutionwas as follows: view of 1ts two mam charactenstics taken together.First, it has an ash content of from 8 to 17 percent by weight which isat least 90 percent iron calculated as Ferric chloride 41.6 gm/liter FeO and second, it has a stable shrink temperature of El i i l2? 3-ycerlne O. at least 200 1 Sodium carbonate 20.8 do.

waaaw. a ...a-.. a. DETAILED DESCRIPTION A small amount of solid mattersettled from theby- The following examples illustrate and demonstrateproduct solution and was removed. One 15 gm. piece specific instances ofthe utility of the invention, showof pickled sheepskin with wool removedwas placed in ing in particular that the combination of ferric iron and.240 ml. portions of each solution and allowed to recitric acid isessential to obtaining good tanning. main there over night at roomtemperature. Both solu- EXAMPLE I This example shows the essentialnature ofthe ironcitions were then adjusted to a pH of 4 with 10 percentsodium carbonate solution. The samples were removed, washed and treatedas in example 1. Both samples of leather appeared to be of high qualityas to color and pliability. The sample treated with laboratory ferricchloride had a shrink temperature of 210 while the product that preparedwith the by-product had one of than a haired hide tanned by a standardchrome tanning method.

Although in the foregoing examples the treatment temperature is ambient,elevated temperatures up to 230F. and their ash contents wererespectively 1 l per- 100F. may be used with the same good results andthe cent and 13 percent. Both samples of ash contained 90 time oftreatment may be correspondingly shortened. percent of iron calculatedas Fe O The discarding of tanning liquors has long raised a EXAMPLEpolution problem. Fortunately the compositions of this This exampleshows that the addition of even sm ll invention are far less toxic thanthe known chromium amounts of glycerine to the solution will improve thecontaining liquors thus aleviating an important aspect shrinktemperature with further improvement being of the problem. Ferricchloride is a relatively cheap obtained with concentrations just overgm./l. Again tanning agent. bated and pickled sheepskin was used and theproce- The product leather of this invention is believed to be dure wasthe same as that in Example I. 5 novel. While others have prepared irontanned leather A B c D E F Volume, ml. 200 220 230 240 250 260 Fecl gms.10 10 10 10 10 10 Cone. gmsJl. 50 45.5 43.5 41.6 40.0 38.5

Citric acid, grns. 5 5 5 5 S 5 Cone. gmS./l. 25.0 22.7 21.7 20.8 20.019.2

Glycerine, gins. 0 2 3 4 S 6 Cone. gmsJl. 0 9.1 13.0 16.7 20.0 23.0

Na co gms. 5 5 5 5 5 5 Cone. gmSJl. 22.7 21.7 20.8 20.0 19.2

P 0.4 Shrink Temperature 200 210 216 212 212 214F EXAMPLE v no recordhas been found of such a leather containing treated in the manner usedin Example 111 but using the solutions listed in the following table.

iron and at the same time exhibiting the high shrink temperaturescharacteristic of the leather described herein in terms of the ashcontent. The ash content varies considerably as shown in the data givenbelow in correspondence with shrink temperatures.

A B C D E F Volume, ml. 200 220 230 240 250 260 FeCl gms. 10 10 10 l0 1010 Cone. gins/l. 50.0 45.5 43.5 41.6 40.0 38.5

Citric Acid, gms. O 3 4 5 6 7 Cone. gmsJl. 0 13.7 17.4 20.8 24.0 27.0

Glycerine, grns. 4 4 4 4 4 4 Cone. gmS./l. 20.0 18.2 17.4 16.7 16.0 15.4

Na CO gms. 5 5 5 5 5 5 Cone. gins-li- 25.0 22.7 21.7 20.8 20.0 19.2

Shrink Temp. F. 208 206 212 :97 202 no substantial evidence of tanningEXAMPLE V Shrink Temp. Ash.

Tanning a pelt An unsheared white sheepskin which had been pick- 200 4'2led but not bated was treated by the tanning solution 35 1;? and methodas described in example 1, Sample A. The 2x6 1 resulting haired leatherwas brown, pliable, and softer 220 13.6

-Continued Shrink Temp.

' ashing to 1000C in air Representative samples of ash were analyzed andfound to contain at least 90 percent by weight of iron calculated as FeO The remainder of the ash is probably residual sodium chloride and/orsodium carbonate. The amount probably depending on the degree ofwashing. Since the ash content of the starting skin is essentially zeroit is believed that with thorough washing and the use of pure ferricchloride, that the ash from the leather would be substantially 100percent ferric oxide.

According to this invention, as illustrated in part by the aboveexamples, a solution of somewhat variable composition is prepared forimpregnating the skin or hide to be tanned. This solution contains, asprimary essential ingredients, from 30 to 70 gms./liter of ferricchloride and from to 35 gms./liter of citric acid. Preferred ranges arefrom 40 to 55 gm./l. of ferric chloride and from 15 to 25 gm./l. ofcitric acid. The piece to be tanned is immersed in this solution untilimpregnated. The temperature of the solution during impregnation shouldnot be above 100F. The solution is, of course, very acid and it ispreferred to reduce its acidity by adding an alkalizing agent such asammonia, sodium carbonate or sodium hydroxide. Only partialneutralization is desired prior to full impregnation of the leather; theextent of neutralization is limited so that the pH value of the solutionis less than about 2.0 and preferably not more than 1. Theneutralization in the range below 2 pH is preferably done beforeimmersion because of potential local heating and high alkalinity whichmight damage the product. Neutralizing agents used at this stage can bein any form such as solid, gas or solution according to the nature ofeach. It is therefore to be understood that the partially neutralizedsolutions are included within the scope of this invention.

Inasmuch as the ferric chloride and citric acid probably will not bepresent in the solution entirely as such, especially after alkalizingagents have been added, the appended claims should be interpreted asincluding all species resulting from the mixing and interaction of theadded essential ingredients. Thus the iron chloride may be converted toferric citrate or various citrate complexes, basic ferric chloride, orcitrates, etc. Similarly the chloride may be present as hydrochloricacid or sodium or ammonium chloride. Therefore, in defining theconcentration of the components of the solutions of this invention interms of ferric chloride, citric acid etc., the definition indicates thechemically equivalent amount of these ingredients present no matter whatform they may take as a result of mixing them together in preparing thesolution. It should be understood also that the alkalizing agents addedalso react and that specified quantities or concentrations of them inthe solution should be interpreted as including the equivalent reactionproducts such as sodium chloride, sodium citrate and the like. In thissense the claimed solution may be said to be composed or consistessentially of the specified added substances.

The impregnation of the skin etc. may require various times depending onthe temperature used, the 7 thickness of the piece and its porosity andthe nature of any agitation used. Preferably the raw leather is immersedin a minimum of the solution for the sake of economy and agitated in amanner that flexes such as tumbling or periodic squeezing. Thesetechniques are common in the leather industry, the mechanics of theprocedure being analogous to those used in chrome tanning.

The action of the above impregnating solutions may be further enhancedby the addition of up to 30 gm./liter, of glycerine and preferably from10 to 25 gms./l.

Ordinary commercial grades of chemicals may be used. In fact it wasfound that ferric chloride obtained as a by-product from the preparationof titanium tetrachloride from ilmenite by chlorination gaveexceptionally good results.

When the desired impregnation of the skin is attained, the solution isneutralized by the addition of sodium carbonate until the pH is in therange of from 3 to 6, preferably near 4.5. This neutralization is doneby ading sodium carbonate, preferably as a 10 percent aqueous solution,to the impregnating solution in the presence of the leather. The use ofsodium carbonate rather than stronger caustic minimizes the heat andlocal alkalinity generated, and is thus substantially harmless to theproduct. The addition of the sodium carbonate is made during agitationand checking the pH until it has become stable at the desired level.This pH adjustment in the 3 to 6 range appears to insolubilize the agentand set the tan. The resulting leather is then washed to remove residualsalts, etc. and finished in known manner.

While the foregoing data is based only on tests with sheepskin, itshould be understood that the novel tanning solution is also applicableto other skins. The testing of tanning methods has customarily beenbased on sheepskin and found to carry over to other materials of similarcollagen content. To test this briefly, samples of rabbit skin and calfskin were treated by the herein described method and found, on the basisof appearance and feel, to have been satisfactorily tanned.

In previous attempts to use iron as a tanning agent in the form of itssulfate salt it was found difficult to remove residual salts which laterhydrolyzed, liberating acid to the detriment of the leather. The methodof this invention is free of this weakness yielding leather having, forexample, a stable shrink temperature. This advantage may be related tothe use of ferric chloride along with citric acid which appears to beuniquely well suited to this process.

The shrink temperature is an important measure of the quality of tanningobtained. Briefly the test involves suspending a weighted strip of theleather sample in a glycerine bath, gradually raising the temperature ofthe bath and noting at what temperature the sample undergoes apronounced shrinking. The procedure is more fully described in Volume 2,page 32 of The Chemistry and Technology of Leather, Fred OFlaherty,Reinhold Publishing Co, 1958 Edition.

I claim 1. An acidic tanning solution consisting essentially of water,from 30 to gms./liter of ferric chloride, and

from to 30 gmsjliter of citric acid.

2. The tanning solution of claim 1 in which the acid has been partiallyneutralized by the addition of an alkalizing agent selected from thegroup consisting of sodium carbonate, ammonia, and sodium hydroxide butis still in the acid range below pH 2.

3. The acidic tanning solution of claim one which also contains from 9.1to 30 grams per liter of glycerme.

4. The tanning solution of claim 3 in which the acid has been partiallyneutralized by the addition of an alkalizing agent selected from thegroup consisting of sodium carbonate, ammonia, and sodium hydroxide but6. The tanning solution of claim 3 in which the acid has been partiallyneutralized by the addition of an alkalizing agent selected from thegroup consisting of sodium carbonate, ammonia, and sodium hydroxide sothat the pH value of said solution is not more than 1.

2. The tanning solution of claim 1 in which the acid has been partiallyneutralized by the addition of an alkalizing agent selected from thegroup consisting of sodium carbonate, ammonia, and sodium hydroxide butis still in the acid range below pH
 2. 3. The acidic tanning solution ofclaim one which also contains from 9.1 to 30 grams per liter ofglycerine.
 4. The tanning solution of claim 3 in which the acid has beenpartially neutralized by the addition of an alkalizing agent selectedfrom the group consisting of sodium carbonate, ammonia, and sodiumhydroxide but is still in the acid range below pH
 2. 5. The tanningsolution of claim 1 in which the acid has been partially neutralized bythe addition of an alkalizing agent selected from the group consistingof sodium carbonate, ammonia, and sodium hydroxide so that the pH valueof said solution is not more than
 1. 6. The tanning solution of claim 3in which the acid has been partially neutralized by the addition of analkalizing agent selected from the group consisting of sodium carbonate,ammonia, and sodium hydroxide so that the pH value of said solution isnot more than 1.